The present invention relates to spinning fibers from thermoplastic polymers. More specifically, the present invention relates to spinning thermoplastic fibers that are colored in the melt, i.e., solution-dyed.
As used herein, certain terms have the meanings ascribed to them.
xe2x80x9cColorantxe2x80x9d means a compound added to impart color to a substrate. Colorants can be, for example, pigments or dyes or mixtures of pigments, dyes, etc.
xe2x80x9cSpiriting efficiencyxe2x80x9d means the percentage of time that the winder is collecting yarn (xe2x80x9cup timexe2x80x9d) with respect to the total operating time, i.e., (up time/total time)xc3x97100.
xe2x80x9cSolution-dyedxe2x80x9d means that color is added to a fiber-forming material prior to extruding it into a fiber through a spinneret capillary.
It is known that, unaided, nylon fibers are not sufficiently light resistant for certain applications. For these nylon fibers, exposure to light causes the fiber to discolor and/or to lose physical properties. Light stabilizers have been incorporated in the nylon polymer to address this problem.
There are several classes of light stabilizers. As additives, organic stabilizers (such as hindered phenols) are expensive and have limited effectiveness.
Inorganic salts are generally less expensive and more effective than organic stabilizers but suffer from a different set of problems. For example, copper compounds are inexpensive relative to organic stabilizers but form copper deposits in pipes, spin packs, extruders and other equipment because some of the copper ions reduce to elemental copper during the spinning process. This phenomenon is described in U.S. Pat. No. 3,929,725 to Davis and U.S. Pat. No. 3,947,424 to Tomek. Copper deposits cause spinning difficulties and add significant equipment maintenance expense. Furthermore, the removal of copper deposits generates environmentally undesirable effluent.
A class of stabilizers is known as xe2x80x9chindered amine light stabilizersxe2x80x9d or by the acronym xe2x80x9cHALSxe2x80x9d. HALS stabilizer additives may be added to the polymer after polymerization in the form of monomers, low molecular weight additives or incorporated into a polymer backbone. Such stabilizers are typically high cost and low effectiveness compared to copper based stablizers. In addition, the polymer itself has been modified by polymerizing the amide monomers in the presence of a HALS type of compound. This has been described in WO 95/28443.
It is known to solution-dye nylon fibers. For example, solution-dyed nylon fibers are described in U.S. Pat. No. 4,374,641 to Burlone. The problem of light stability is complicated by solution-dyeing. Some colorants actually accelerate the degradation of the host polyamide. Without stabilizing additives, the fiber loses an unacceptable degree of strength during exposure to light or the colorant does not remain xe2x80x9ctruexe2x80x9d to its color. Proper stabilizer selection is made tricky, to say the least. For example, certain pigments are taught to be incompatible with HALS stabilizers. See W. Herbst and K. Hunger, xe2x80x9cIndustrial Organic Pigmentsxe2x80x9d Verlagsgesellschaft mbH, Federal Republic of Germany, 1993, pp. 467-475.
Although WO 95/28443 describes addition of TiO2 and possibly other colorants, this addition is during the polymerization phase. In the manufacture of a palette of solution-dyed yarns, it is not practical to use polymer that is already colored (not delustered) in polymerization. It should be apparent that the color of the polymer will interfere with the fiber spinner""s ability to make a broad spectrum of colors.
In addition, certain colorants or classes of colorants are notoriously difficult to spin and operators experience frustating breaks during the spinning process. Any method that improves the spinning efficiency of solution-dyed fibers colored with these materials is desirable.
Therefore, there remains a need for an inexpensive method for making a variety of colors in solution-dyed nylon fibers that are stabilize with respect to the polyamide and to the colorant. Such a method should not have any of the disadvantages that are described above.
It is an object of the present invention to provide a process for making a light stabilized solution-dyed fiber.
It is another object of the present invention to provide improved efficiency for traditionally difficult to spin solution-dyed fibers.
A further object of the present invention is to eliminate or significantly reduce stabilizer build-up in melt spinning lines.
A still further objective of the present invention is to provide a light stabilized solution-dyed fiber.
Yet, another object of the present invention is to provide an environmentally-friendly, efficient process for producing solution-dyed nylon fibers.
These object are achieved in a process for making stabilized, solution-dyed fiber by melting a polyamide which is amide monomers polymerized in the presence of at least one hindered piperidine compound having the formula: 
where R1, R2, R3 and R4 are not hydrogen, but are any alkyl group having up to about 20 carbon atoms, and R5, R6, R7 and R8 are any alkyl group having up to 20 carbon atoms or hydrogen and, optionally, at least one mono or dicarboxylic acid chain regulator; and coloring the melted polyamide with a colorant selected from the group consisting of: pigments that are not pure iron oxide pigments; dyes; and mixtures thereof.
The colored polyamide is spun into fibers that have about 40% or better retained tenacity after 2125 kJ exposure to xenon arc radiation as per AATCC Test Method 16-1993, xe2x80x9cColorfastness to Light,xe2x80x9d Option E and that contain no more than about 10 ppm uncomplexed copper.
In another aspect, the present invention includes a light stabilized solution-dyed nylon fiber. The fiber is a polyamide host polymer which is amide monomers polymerized in the presence of at least one hindered piperidine compound having the formula: 
where R1, R2, R3 and R4 are not hydrogen, but are any alkyl group having up to about 20 carbon atoms, and R5, R6, R7 and R8 are any alkyl group having up to about 20carbon atoms or hydrogen and, optionally, at least one mono or dicarboxylic acid chain regulator; and a non-white colorant dispersed throughout the host polymer. Such fiber is substantially free from copper compounds.
Related object and advantages of the present invention will be apparent to those of ordinary skill in the art after reading the following detailed description.